1. Field of the Invention
The present invention relates to a fuel cell system and a gas-liquid separation system for the fuel cell system.
2. Description of the Related Art
A direct fuel cell that directly supplies liquid fuel such as alcohol to a power generation unit does not require auxiliaries such as an evaporator and a reformer. Accordingly, it is expected that the direct fuel cell will be used for such as a small power supply of a portable instrument. For example, a direct methanol fuel cell (DMFC) includes a cell stack (electromotive unit) in which a plurality of single cells, each of which has an anode and a cathode, are stacked on one another. In the electromotive unit, diluted methanol is supplied to an anode side, and the air is supplied to a cathode side, whereby a chemical reaction is caused to generate power. As a result, a gas-liquid two-phase flow containing unreacted methanol and carbonic acid gas is discharged from the anode side, and water is discharged from the cathode side.
The gas-liquid two-phase flow discharged from the anode side is fed to a fuel tank through a collection passage and the like, and is adjusted into a methanol solution with the optimum concentration for the power generation in the fuel tank connected to the collection passage. Thereafter, the methanol solution is circulated to the anode side of the electromotive unit. In order to efficiently reuse the gas-liquid two-phase flow discharged from the anode side, it is necessary, in advance, to separate the carbonic acid gas from the gas-liquid two-phase flow and to discharge the separated carbonic acid gas so that the carbonic acid gas contained in the gas-liquid two-phase flow cannot be circulated to the anode side. As a method of separating and discharging the carbonic acid gas, for example, there is known a method of providing a gas-liquid separator, in which a gas-liquid separation membrane is disposed, in a passage on an anode outlet side (for instance, refer to JP-A No. 2005-238217 (KOKAI)).
However, since a vapor phase discharged from the gas-liquid separation membrane contains steam, in some case, the steam that has flown out through the gas-liquid separation membrane fills a space in the gas-liquid separator, causing condensation. In particular, a temperature of the gas-liquid two-phase flow discharged from the electromotive unit is higher than room temperature, and in addition, a moisture content of the steam is large. Accordingly, the condensation occurs in the gas-liquid separator unless a temperature of the gas-liquid separator is set higher than the temperature of the gas-liquid two-phase flow.